Flexible therapy electrode

ABSTRACT

An electrode assembly includes a first surface to be placed adjacent a person&#39;s skin and a second surface including a plurality of reservoirs of conductive gel. The plurality of reservoirs of conductive gel are disposed on sections of the electrode assembly that are at least partially physically separated and may move at least partially independently of one another to conform to contours of a body of a patient. The electrode assembly is configured to dispense an amount of the electrically conductive gel onto the first surface in response to an activation signal and to provide for a defibrillating shock to be applied to the patient through the amount of the electrically conductive gel.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed to medical electrodes, and moreparticularly, to flexible medical electrodes that may be used with awearable medical device, such as a defibrillator.

2. Discussion of Related Art

Cardiac arrest and other cardiac health ailments are a major cause ofdeath worldwide. Various resuscitation efforts aim to maintain thebody's circulatory and respiratory systems during cardiac arrest in anattempt to save the life of the victim. The sooner these resuscitationefforts begin, the better the victim's chances of survival. Theseefforts are expensive and have a limited success rate, and cardiacarrest, among other conditions, continues to claim the lives of victims.

To protect against cardiac arrest and other cardiac health ailments,some at-risk patients may use a wearable defibrillator, such as theLifeVest® wearable cardioverter defibrillator available from ZOLLMedical Corporation of Chelmsford, Mass. To remain protected, thepatient wears the device nearly continuously while going about theirnormal daily activities, while awake, and while asleep.

SUMMARY

In accordance with an aspect of the present invention, there is providedan electrode system. The electrode system comprises a substrateincluding a plurality of conductive gel reservoirs disposed on a firstside thereof, a first of the plurality of conductive gel reservoirsdisposed in a first segment of the substrate and a second of theplurality of the conductive gel reservoirs disposed in a second segmentof the substrate, a fluid channel in fluid communication with a fluidsource, the first of the plurality of conductive gel reservoirs, and thesecond of the plurality of the conductive gel reservoirs, and one of aslot or a gap defined in the substrate and extending from a regionproximate the fluid channel and between the first of the plurality ofconductive gel reservoirs and the second of the plurality of theconductive gel reservoirs to an edge of the substrate distal from thefluid channel. The one of the slot or the gap physically separates atleast a portion of the first segment of the substrate from the secondsegment of the substrate.

In accordance with some embodiments, the electrode system furthercomprises an electrically conductive layer having a first surfacedisposed on a second side of the substrate and having a second surfaceconfigured to be disposed adjacent to a patient's skin.

In accordance with some embodiments, the plurality of conductive gelreservoirs and the fluid channel are included in a first impedancereduction system configured to dispense a first amount of a firstelectrically conductive gel onto the second surface of the electricallyconductive layer in response to a first activation signal, and whereinthe electrode system further includes a second impedance reductionsystem configured to dispense a second amount of a second electricallyconductive gel onto the second surface of the electrically conductivelayer in response to a second activation signal.

In accordance with some embodiments, the first impedance reductionsystem is similar in construction to the second impedance reductionsystem.

In accordance with some embodiments, the electrode system furthercomprises a garment wearable on a torso of a patient, the garmentincluding a pocket formed from a layer of fabric and configured toreceive the electrode system, wherein the electrode system is configuredto dispense an amount of a conductive gel through the layer of fabricand into contact with the patient's skin.

In accordance with some embodiments, the electrode system furthercomprises an electrically conductive layer disposed on a second side ofthe substrate, the electrically conductive layer including a pluralityof apertures configured to dispense the amount of the conductive gel.

In accordance with some embodiments, the electrode system furthercomprises an electrically conductive pathway included in the layer offabric, the electrically conductive pathway configured to deliverelectrical energy to the patient's skin through the amount of conductivegel dispensed from the electrode system.

In accordance with some embodiments, the layer of fabric is formed froman electrically conductive material.

In accordance with some embodiments, each of the substrate and thepocket are tapered to permit the electrode system to be received in thepocket in only a single orientation.

In accordance with some embodiments, the electrode system furthercomprises at least one ECG sensing electrode configured to monitor anECG signal of a patient, the at least one ECG sensing electrode beingdisposed on a second side of the substrate and electrically insulatedfrom portions of the electrode system configured to receive conductivegel.

In accordance with some embodiments, the electrode system furtherincludes at least one additional sensor configured to monitor aphysiological parameter of the patient other than an ECG signal of thepatient.

In accordance with some embodiments, the at least one additional sensoris disposed on a third segment of the substrate, the third segment ofthe substrate at least partially physically separated by one of a slotor a gap defined in the substrate from portions of the substrate onwhich the plurality of conductive gel reservoirs are disposed.

In accordance with some embodiments, the substrate further comprises aplurality of additional segments positioned adjacent to one another andat least partially physically separated from one or another by slots orgaps defined in the substrate, each of the plurality of additionalsegments including a conductive gel reservoir disposed on first sidethereof.

In accordance with some embodiments, the fluid pressure source isdisposed on a third segment of the substrate, the third segment of thesubstrate being at least partially physically separated by one of a slotor a gap defined in the substrate from portions of the substrate onwhich the plurality of conductive gel reservoirs are disposed.

In accordance with some embodiments, the substrate is tapered from afirst end to a second end, the taper of the substrate preventinginsertion of the electrode system into a tapered pocket of a wearablemedical device in an undesired direction.

In accordance with some embodiments, the electrode system furthercomprises a magnet disposed on a portion of the substrate and configuredto apply a force to a magnet disposed on a pocket of a garment in whichthe electrode system can be inserted, the applied force providing anindication of proper orientation of the electrode system in the pocket.

In accordance with some embodiments, the electrode system furthercomprises a snap disposed on a portion of the substrate and configuredto engage a corresponding snap disposed on a pocket of a garment inwhich the electrode system can be inserted, the engagement of the snapwith the corresponding snap providing an indication of properorientation of the electrode system in the pocket.

In accordance with some embodiments, the substrate comprises a fabricpermeable to conductive gel which the electrode assembly is configuredto dispense.

In accordance with some embodiments, the substrate is perforated.

In accordance with some embodiments, the electrode system includes anindicator disposed on an externally visible surface of the electrodesystem and configured to visually indicate whether the fluid source hasbeen actuated.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are not intended to be drawn to scale. In thedrawings, each identical or nearly identical component that isillustrated in various figures is represented by a like numeral. Forpurposes of clarity, not every component may be labeled in everydrawing. In the drawings:

FIG. 1 illustrates a wearable medical device, such as a wearabledefibrillator;

FIG. 2A is a top plan view of a therapy electrode assembly that may beused with the wearable medical device illustrated in FIG. 1;

FIG. 2B is a functional block diagram of an impedance reduction systemthat may be included in the therapy electrode assembly of FIG. 2A;

FIG. 2C is a bottom plan view of an electrode portion of the therapyelectrode assembly of FIG. 2A;

FIG. 3A is a top plan view of an electrode portion of a therapyelectrode assembly that may be used with the wearable medical deviceillustrated in FIG. 1;

FIG. 3B is a bottom plan view of an electrode portion of a therapyelectrode assembly that may be used with the wearable medical deviceillustrated in FIG. 1;

FIG. 3C is a top plan view of another electrode portion of a therapyelectrode assembly that may be used with the wearable medical deviceillustrated in FIG. 1;

FIG. 3D is a top plan view of a therapy electrode assembly that may beused with the wearable medical device illustrated in FIG. 1;

FIG. 3E is a top plan view of a therapy electrode assembly that may beused with the wearable medical device illustrated in FIG. 1;

FIG. 4 is a cross sectional view of an electrode portion a therapyelectrode assembly that may be used with the wearable medical deviceillustrated in FIG. 1 applied to fabric against the skin of a patient;

FIG. 5 is an elevational view of a therapy electrode assembly that maybe used with the wearable medical device illustrated in FIG. 1;

FIG. 6A illustrates placement of therapy electrode assemblies in a rearportion of a wearable medical device;

FIG. 6B illustrates placement of a therapy electrode assembly in a frontportion of a wearable medical device;

FIG. 6C is a plan view of the rear of a wearable medical deviceincluding tapered pockets for therapy electrode assemblies;

FIG. 7 is an exploded view of a pocket of a wearable medical device andtherapy electrode assembly intended to reside within the pocket;

FIG. 8 is a functional block diagram of a redundant impedance reductionsystem in accordance with an aspect of the present invention;

FIG. 9 is a schematic diagram of an electrode assembly that includes ECGsensing electrodes, a therapy electrode, and redundant impedancereduction systems in accordance with another aspect of the presentinvention; and

FIG. 10 illustrates a manner in which the electrode assembly of FIG. 9may be worn on the body of a patient.

DETAILED DESCRIPTION

This invention is not limited in its application to the details ofconstruction and the arrangement of components set forth in thefollowing description or illustrated in the drawings. The invention iscapable of other embodiments and of being practiced or of being carriedout in various ways. Also, the phraseology and terminology used hereinis for the purpose of description and should not be regarded aslimiting. The use of “including,” “comprising,” “having,” “containing,”“involving,” and variations thereof herein is meant to encompass theitems listed thereafter and equivalents thereof as well as additionalitems.

FIG. 1 illustrates a wearable medical device, such as a LifeVest®wearable cardioverter defibrillator available from ZOLL MedicalCorporation of Chelmsford, Mass. As shown, the wearable medical device100 includes a harness 110 having a pair of shoulder straps and a beltthat is worn about the torso of a patient. The harness 110 is typicallymade from a material, such as cotton, that is breathable, and unlikelyto cause skin irritation, even when worn for prolonged periods of time.The wearable medical device 100 includes a plurality of ECG sensingelectrodes 112 that are attached to the harness 110 at various positionsabout the patient's body and electrically coupled to a control unit 120via a connection pod 130. The plurality of ECG sensing electrodes 112,which may be dry-sensing capacitance electrodes, are used by the controlunit 120 to monitor the cardiac function of the patient and generallyinclude a front/back pair of ECG sensing electrodes and a side/side pairof ECG sensing electrodes. Additional ECG sensing electrodes may beprovided, and the plurality of ECG sensing electrodes 112 may bedisposed at varying locations about the patient's body.

The wearable medical device 100 also includes a plurality of therapyelectrodes 114 that are electrically coupled to the control unit 120 viathe connection pod 130 and which are capable of delivering one or moretherapeutic defibrillating shocks to the body of the patient, if it isdetermined that such treatment is warranted. As shown, the plurality oftherapy electrodes 114 includes a first therapy electrode 114 a that isdisposed on the front of the patient's torso and a second therapyelectrode 114 b that is disposed on the back of the patient's torso. Thesecond therapy electrode 114 b includes a pair of therapy electrodesthat are electrically coupled together and act as the second therapyelectrode 114 b. The use of two therapy electrodes 114 a, 114 b permitsa biphasic shock to be delivered to the body of the patient, such that afirst of the two therapy electrodes can deliver a first phase of thebiphasic shock with the other therapy electrode acting as a return, andthe other therapy electrode can deliver the second phase of the biphasicshock with the first therapy electrode acting as the return. Theconnection pod 130 electrically couples the plurality of ECG sensingelectrodes 112 and the plurality of therapy electrodes 114 to thecontrol unit 120, and may include electronic circuitry. For example, inone implementation the connection pod 130 includes signal acquisitioncircuitry, such as a plurality of differential amplifiers to receive ECGsignals from different ones of the plurality of ECG sensing electrodes112 and to provide a differential ECG signal to the control unit 120based on the difference therebetween. The connection pod 130 may alsoinclude other electronic circuitry, such as a motion sensor oraccelerometer by which patient activity may be monitored.

As shown in FIG. 1, the wearable medical device 100 also includes a userinterface pod 140 that is electrically coupled to the control unit 120.The user interface pod 140 can be attached to the patient's clothing orto the harness 110, for example, via a clip (not shown) that is attachedto a portion of the interface pod 140. Alternatively, the user interfacepod 140 may simply be held in a person's hand. In some embodiments, theuser interface pod 140 may communicate wirelessly with the control unit120, for example, using a Bluetooth®, Wireless USB, ZigBee, WirelessEthernet, GSM, or other type of communication interface. The userinterface pod 140 typically includes a number a number of buttons bywhich the patient, or a bystander can communicate with the control unit120, and a speaker by which the control unit 120 may communicate withthe patient or the bystander. For example, where the control unit 120determines that the patient is experiencing cardiac arrhythmia, thecontrol unit 120 may issue an audible alarm via a loudspeaker (notshown) on the control unit 120 and/or the user interface pod 140alerting the patient and any bystanders to the patient's medicalcondition. The control unit 120 may also instruct the patient to pressand hold one or more buttons on the control unit 120 or on the userinterface pod 140 to indicate that the patient is conscious, therebyinstructing the control unit 120 to withhold the delivery of one or moretherapeutic defibrillating shocks. If the patient does not respond, thedevice may presume that the patient is unconscious, and proceed with thetreatment sequence, culminating in the delivery of one or moredefibrillating shocks to the body of the patient. In some embodiments,the functionality of the user interface pod 140 may be integrated intothe control unit 120.

The control unit 120 generally includes at least one processor,microprocessor, or controller, such as a processor commerciallyavailable from companies such as Texas Instruments, Intel, AMD, Sun,IBM, Motorola, Freescale and ARM Holdings. In one implementation, the atleast one processor includes a power conserving processor arrangementthat comprises a general purpose processor, such as an Intel® PXA270processor and a special purpose processor, such as a Freescale DSP56311Digital Signal Processor. Such a power conserving processor arrangementis described in co-pending U.S. patent application Ser. No. 12/833,096,titled SYSTEM AND METHOD FOR CONSERVING POWER IN A MEDICAL DEVICE, filedJul. 9, 2010 which is incorporated by reference herein in its entirety.The at least one processor of the control unit 120 is configured tomonitor the patient's medical condition, to perform medical data loggingand storage, and to provide medical treatment to the patient in responseto a detected medical condition, such as cardiac arrhythmia. Althoughnot shown, the wearable medical device 100 may include additionalsensors, other than the ECG sensing electrodes 112, capable ofmonitoring the physiological condition or activity of the patient. Forexample, sensors capable of measuring blood pressure, heart rate,thoracic impedance, pulse oxygen level, respiration rate, heart sounds,and the activity level of the patient may also be provided.

As discussed above, to provide protection against cardiac arrest,patients that use a wearable medical device, such as a wearabledefibrillator, generally wear the device nearly continuously while theyare awake and while they are asleep. Because the wearable medical deviceis worn nearly continuously, dry electrodes are typically used for boththe plurality of ECG sensing electrodes 112 and the plurality of therapyelectrodes 114 for comfort and to prevent irritation of the patient'sskin. Where it is determined that one or more defibrillating shocks areto be delivered to the body of the patient and the patient isnon-responsive, the control unit 120 sends a signal to the plurality oftherapy electrodes 114 causing them to release an impedance reducing gelprior to delivery of one or more defibrillating shocks. The impedancereducing gel reduces the impedance between the conductive surface of thetherapy electrodes and the patient's skin, thereby improving theefficiency of the energy delivered to the patient and reducing thechance of damage (e.g., in the form of burning, reddening, or othertypes of irritation) to the patient's skin.

FIG. 2A is a plan view of a therapy electrode assembly 200 that includesan impedance reduction system and which may be used with a wearablemedical device, such as the wearable defibrillator described above withrespect to FIG. 1. FIG. 2B is a functional block diagram of impedancereduction system 201 that is included in the therapy electrode assembly200 shown in FIG. 2A. The impedance reduction system 201, whenactivated, dispenses an impedance reducing (i.e., electricallyconductive) gel onto the exposed surface of the therapy electrodeassembly that, in use, is placed most proximate to the patient's body.The therapy electrode assembly 200 is a multiple layer laminatedstructure that includes an electrically conductive layer disposedadjacent the bottom surface of the therapy electrode assembly 200 and animpedance reduction system 201. The electrically conductive layer formsthe electrode portion 202 of the therapy electrode assembly 200 as shownin FIG. 2C. In use, the electrically conductive layer is disposedadjacent the patient's skin, although the conductive layer need not makedirect contact with the patient. For example, portions of the harness110 (FIG. 1) may be present between the electrically conductive layerand the patient's skin. As shown in FIG. 2A, the impedance reductionsystem 201 is disposed on a side of the therapy electrode assembly 200(i.e., the top-side shown in FIG. 2A) that is opposite the side on whichthe conductive layer is formed.

The impedance reduction system 201 includes a plurality of conductivegel reservoirs 210, each of which has a respective gel delivery outlet220, that are fluidly coupled to a fluid channel 230, and a fluidpressure source 240. The fluid pressure source 240 is fluidly coupled tothe fluid channel 230, and when activated by an activation signal,forces a fluid, such as nitrogen gas, into the channel 230. Thehydraulic pressure of the fluid from the activated fluid pressure source240 in the fluid channel 230 forces the conductive gel stored in each ofthe plurality of gel reservoirs out of the plurality of gel deliveryoutlets 220 through apertures formed in the bottom surface of theelectrode portion 202 and onto the exposed bottom surface of theelectrode portion 202. The apertures are generally aligned with theplurality of gel delivery outlets 220 so that when activated, theelectrically conductive gel is dispensed onto the exposed surface of theelectrode portion that is disposed most proximate to the patient's body.Further details regarding the construction of the therapy electrodeassembly 200 are described in U.S. Pat. No. 5,078,134 (hereinafter “the'134 patent”) which is incorporated herein by reference in its entirety.

To perform effectively, it is desirable that the therapy electrodeportion 202 be configured to conform to a variety of body contours andshapes so that in use, a significant, or in some embodiments,substantially an entire area of the bottom surface (the surface to be incontact with or positioned proximate a patient's body) of the electrodeportion 202 is in intimate contact with a patient's body or with thefabric of a garment worn by the patient, for example, the wearablemedical device 100 of FIG. 1. As a patient goes through daily routinesincluding walking, sitting, sleeping, or performing other tasks, thepatient's body shape and contours where a therapy electrode ispositioned may be subject to various degrees of deformation. A therapyelectrode may thus desirably be flexible and shape conforming tofacilitate maintaining contact between a surface of the therapyelectrode and a patient's body or garment.

Conventional therapy electrodes have traditionally been formed on asingle non-segmented substrate which in some instances includes aflexible metal material or a polymeric material with a layer of metallicmaterial deposited thereon.

FIGS. 3A-3E illustrate embodiments of a therapy electrode assembly 300which may provide be more flexible and facilitate maintaining a greateramount of contact between a surface of the therapy electrode and apatient's body or garment than a conventional therapy electrodeassembly. The substrate 305 of the electrode portion 302 of a therapyelectrode assembly illustrated in FIGS. 3A-3E is divided into multipleconnected segments 305 a. The multiple segments 305 a may move at leastpartially independently from one another. Each of the segments 305 a mayinclude at least one conductive gel reservoir 310 and at least one geldelivery outlet 320, which may be similar in construction and functionas the gel reservoirs 210 and gel delivery outlets 220 described above.The various segments 305 a may be at least partially physicallyseparated from one another by, for example, one or more of a slot 315 a,a gap 315 b, or other open area between adjacent segments 305 a. Thevarious segments 305 a may be physically coupled together by a centralspine including one or more fluid conduits 330 configured to deliverfluid to the conductive gel reservoirs 310 to cause the release ofconductive gel therefrom.

As illustrated, the slots 315 a and/or gaps 315 b may extend from acentral portion of the substrate 305 of the therapy electrode assembly300 proximate a central fluid conduit 330 and between adjacent segments305 a to an edge of the substrate 305. Providing for the varioussegments 305 a of the electrode portion to move at least partiallyindependently of one another may facilitate conformance of the electrodeportion 302 to curves or contours of a patient's body. A segmentedelectrode portion 302 as illustrated in FIG. 3B may provide for agreater area, or a greater percentage of the total area, of theelectrode portion to be in contact with the patient's body than if theelectrode portion 302 were formed of a single, non-segmented substrate,such as illustrated in, for example, FIG. 2C.

In some embodiments, a segment 305 b of a therapy electrode including afluid pressure source 340 or other features, for example, an ECGelectrode or a sensor for some other parameter indicative of a patient'smedical condition may be at least partially physically separated fromone or more of the segments 305 a. This partial physical separation maybe provided by including a slot 315 a, a gap 315 b, or other open areabetween a portion of the therapy electrode assembly 300 including thegel reservoirs 310 and the segment 305 b of the therapy electrodeassembly including the fluid pressure source 340 or other feature(s). Insome embodiments, the segment 305 b may be connected to the segments 305a by a fitting, for example, a tube 330 a of a first diameter coupled toone of the segments 305 a and 305 b inserted into the bore of a tube 330b of a second diameter coupled to the other of the segments 305 a and305 b, such as shown in FIG. 3C. Such a construction provides for thesegment 305 b to rotate relative to the segments 305 a and may providefor a reduced tendency for the segment 305 b of the electrode toconstrain movement of the one or more segments 305 a including the gelreservoirs 310.

As one of ordinary skill in the art would recognize, the shapes andpositions of the segments 305 a and 305 b and of the slots 315 a and/orgaps 315 b may be provided in different configurations from thoseillustrated in FIG. 3A. For example, the various segments 305 a mayinclude rounded or squared ends or have different aspect ratios thanillustrated. The slots 315 a and/or gaps 315 b may be curved asillustrated in FIG. 3A, squared as illustrated in FIG. 3D, or mayinclude re-entrant portions 315 c extending between one of the gelreservoirs 310 and gel delivery outlets 320 and a portion of the fluidconduit 330 as illustrated in FIG. 3E.

In some embodiments, the electrode portion 302 may include a metalizedor otherwise conductive film on a portion of, or an entirety of, thebottom side of the electrode portion which is to be positioned againstor face the skin of a patient. Prior to a defibrillating shock beingdelivered to the patient, conductive gel may be released from the gelreservoirs 310 to form a low impedance conductive path between themetalized side of the electrode portion 302 and the skin of the patient.Current may be applied through the metalized side of the electrodeportion, the conductive gel, and the skin of the patient.

In other embodiments, the therapy electrode assembly 300 does notinclude a conductive film forming an electrode portion 302 on the bottomside of the electrode assembly 300 to be positioned against or face theskin of a patient. The majority of, or the entirety of the bottomsurface of the electrode assembly 300 facing the skin of the patient maybe substantially or completely non-conductive. Current may be applied tothe patient to deliver a defibrillating shock by a method which does notinvolve passing current through or along any surface of the electrodeassembly.

For example, as illustrated in FIG. 4, a therapy electrode assembly 300having no conductive material present on the surface 350 facing the skin360 of a patient may be disposed in a pocket in a garment worn by thepatient or otherwise secured to an external surface of the garment. Asused herein, the term “garment” includes clothing, for example, a shirtor jacket, as well as wearable medical devices, for example, a LifeVest®wearable cardioverter defibrillator.

The substrate 305 of the therapy electrode assembly 300 may be formed ofa natural or synthetic fabric, for example, cotton, wool, or polyester.In instances where the substrate is not waterproof, the gel reservoirs210, 310 may be formed with a membrane, for example, a plastic film,where the gel reservoirs contact the fabric to facilitate retainingconductive gel within the gel reservoirs and prevent it from escapingthrough the substrate. In other embodiments, the fabric may include awaterproof coating where the gel reservoirs 210, 310 contact the fabric.Forming the substrate 305 out of a fabric material may provide for thesubstrate to easily conform to the contours of the body of a patient.The substrate 305 may include perforations. Forming the substrate 305out of a fabric material and/or with perforations may facilitate passageof conductive gel through the substrate upon release of the conductivegel from the gel reservoirs 210, 310.

Fabric 370 of the garment between the surface 350 of the therapyelectrode assembly 300 and the skin 360 of the patient may be conductiveand/or may include conductive stitching 380. Upon release of conductivegel from the gel reservoirs 310 through the gel delivery outlets 320,the conductive gel may pass through the weave of the fabric 370 and maycontact the conductive stitching 380 and the skin 360 of the patient onthe opposite side of the garment fabric 370 from the surface 350. Thereleased conductive gel may form a low impedance conductive path betweenthe conductive stitching 380 or conductive fabric of the garment and theskin 360 of the patient. A defibrillating shock may be delivered to thepatient through the conductive stitching 380 or conductive fabric of thegarment and through the released conductive gel into the skin of thepatient.

The therapy electrode assembly 300 may be provided with a relativelylarge, easy-to-grip pull tab 495 (illustrated in FIG. 5) to facilitateinsertion or removal of the therapy electrode assembly 300 from a pocketof a garment or wearable medical device. In accordance with oneembodiment, the pull tab 495, or another visible surface of the therapyelectrode assembly may include an indicator that identifies whether theimpedance resistance system has been activated or not. Such indicatorsmay include, for example, an additional gel reservoir coupled to thefluid channel which may release a dye or other colored substance uponactivation of the impedance reduction system. The indicator may alsoinclude, for example, a section of wiring, or a fuse or other devicewhich may change color responsive to the application of electricalenergy to the electrode. Other indicator devices known to those in theart are also contemplated and embodiments of the present invention arenot limited to any particular indicator device.

Therapy electrode assemblies in accordance with various embodiments mayinclude one or more features which facilitate proper insertion of thetherapy electrode assembly into a garment to be worn by a patient. Forexample, as illustrated in FIG. 5, a therapy electrode assembly 400 maybe formed with a tapered shape. A first end 485 of the therapy electrodeassembly 400, for example, an end proximate the fluid pressure source(not visible in FIG. 5), when present, may be wider than a second end490 of the therapy electrode assembly 400, for example, an end distalfrom the fluid pressure source. The provision of corresponding taperedpockets 510 on a wearable medical device 100 as illustrated in FIGS. 6Aand 6B (where the fabric overlying the therapy electrode assemblies isremoved for clarity) allows therapy electrode assemblies 400 to beinserted only tapered end first. FIG. 6C illustrates a rear side of awearable medical device 100 including tapered pockets 510 in whichtapered therapy electrode assemblies may be placed and which may limitthe direction in which the tapered therapy electrode assemblies areinserted.

The shape of tapered therapy electrode assemblies 400 are not limited tothat illustrated in the figures. In some embodiments, both edges of atherapy electrode assembly 400 may be tapered and in other embodimentsonly a single edge is tapered. The degree of taper on each edge of atherapy electrode assembly 400 may differ. In some embodiments, aportion of one or both edges of a therapy electrode assembly 400 mayinclude a cut out portion, which may be, for example, rectangular,instead of a gradually tapering profile as illustrated. A therapyelectrode assembly 400 in accordance with embodiments of the presentinvention may be shaped in any manner which may facilitate insertion ofthe therapy electrode into the pocket in a correct orientation.

An additional feature which may facilitate proper insertion of thetherapy electrode assembly into a garment to be worn by a patient isillustrated in FIG. 7, which is an exploded view of portions of a pocketof a garment and a therapy electrode assembly 500 intended to be placedwithin the pocket. The therapy electrode assembly 500 of FIG. 7 includestwo magnets 520 located on the substrate 515. Corresponding magnets 530may be located on material forming inner and/or outer portions 540, 550,respectively, or both, of a pocket of a wearable medical device 100 intowhich the therapy electrode assembly 500 is to be inserted. The magnets520, 530 may be arranged such that the magnets 530 in the material ofthe pocket will be repelled from the magnets 520 in the substrate unlessthe therapy electrode assembly 500 is inserted properly, for example,with the side onto which the conductive gel is to be released facing theside of the pocket against the skin of a patient. For example, each ofthe magnets 520 could be arranged with North poles facing in a directionaway from an electrode side of the therapy electrode assembly 500 andSouth poles facing in an intended direction of the body of a patientwearing the wearable medical device 100. The fabric of the outer portionof the pocket could then include magnets with North poles facing inwardtoward the side of the garment intended to lie against the skin of thepatient. The fabric of the inner portion of the pocket could includemagnets with South poles facing away from the side of the garmentintended to lie against the skin of the patient. Unless the magnets wereattracted to each other and “clicked” together, a patient would knowthat the therapy electrode assembly 500 was not properly inserted intothe pocket. Fewer or greater than two magnets may be included in any ofthe therapy electrode assembly 500 and either one or both of the innerand outer portions 540, 550, respectively, of the pocket of the wearablemedical device 100. The orientation of the poles of the magnets could bealtered as desired.

In alternate embodiments, one or more of the magnets 520, 530 may bereplaced or supplemented by snaps having male sides and female sides.For example, a female side of a snap may be placed on the surface of theupper side (the side intended to face away from a patient) of thesubstrate. A corresponding male half of the snap may be provided on theinternal surface of fabric of an outer layer of a pocket of a wearablemedical device 100 into which the therapy electrode assembly 500 isintended to be inserted. The male and female portions of the snap wouldonly be able to engage if the therapy electrode assembly 500 wasinserted into the pocket in the correct orientation. Other directionalsnaps or fasteners having male and female sides, for example, hook andloop fasteners, may also or alternatively be used.

Applicants have appreciated that there may be instances where it wouldbe desirable to have redundancy in the impedance reduction systemdescribed above. An electrode that incorporates redundant impedancereduction systems is now described with respect to FIGS. 8-10 below.

FIG. 8 is a functional block diagram of a redundant impedance reductionsystem that may be incorporated into a therapy electrode assembly inaccordance with an aspect of the present invention. As shown, theredundant impedance reduction system 600 includes at least twoindependent impedance reduction systems 601, 602 similar in constructionand operation to that described previously with respect to FIGS. 3A-3E.Although only two impedance reduction systems 601, 602 are shown in FIG.8, it should be appreciated that additional impedance reduction systemsmay be provided.

As shown, a first impedance reduction system 601 of the at least twoimpedance reduction systems 601, 602 includes a first plurality of gelreservoirs 610 a, each containing an electrically conductive gel, witheach respective gel reservoir including a gel delivery outlet 620 a.Each of the first plurality of gel reservoirs 610 a is fluidly coupledto a first fluid channel 630 a that is, in turn, fluidly coupled to afirst fluid pressure source 640 a. The first fluid pressure source 640 ahas an input 641 a to receive a first electrical activation signal and afluid outlet 642 a that is fluidly coupled to the first fluid channel630 a. A rupturable membrane and/or a filter (not shown) may bepositioned between the fluid outlet 642 a and the first fluid channel630 a as described in the '134 patent. As described in the '134 patent,the first fluid pressure source 640 a may include a gas generatingcartridge that ignites a chemical pellet (such as a lead styphnateigniter and a gas generating mixture of ammonium dichromate andnitroguanidine) that rapidly decomposes and generates quantities of agas, such as nitrogen. It should be appreciated that other types offluid pressure sources may be used, as the present invention is notlimited to any particular type of fluid pressure source.

In response to the first activation signal received at the input 641 aof the first fluid pressure source 640 a, a fluid, such as nitrogen gas,is forced into the first fluid channel 630 a and then into each of thefirst plurality of gel reservoirs 610 a. The hydraulic pressure of thefluid flowing into each of the first plurality of gel reservoirs 610 aforces the electrically conductive gel contained in each gel reservoirtoward its respective gel delivery outlet 620 a, thereby fracturing amembrane separating the gel delivery outlet from a respective apertureformed in the electrically conductive layer of the electrode portion.

The second impedance reduction system 602 of the at least two impedancereduction systems 601, 602 is similar to the first impedance reductionsystem 601 and includes a second plurality of gel reservoirs 610 b, eachcontaining an electrically conductive gel, with each respective gelreservoir including a gel delivery outlet 620 b. The electricallyconductive gel contained in the second plurality of gel reservoirs 610 bmay, but need not, be the same type of gel as that contained in thefirst plurality of gel reservoirs 610 a. For example, the electricallyconductive gel contained in the second plurality of gel reservoirs 610 bmay have a different color, or have a longer drying time than the gelcontained in the first plurality of gel reservoirs 610 a. Each of theplurality of gel reservoirs 610 b is fluidly coupled to a second fluidchannel 630 b that is, in turn, fluidly coupled to a second fluidpressure source 640 b. The second fluid pressure source 640 b has aninput 641 b to receive a second electrical activation signal and a fluidoutlet 642 b that is fluidly coupled to the second fluid channel 630 b.The second fluid pressure source 640 b may similar in construction tothe first fluid source 640 a described above.

As shown in FIG. 8, the input 641 a of the first fluid pressure source640 a may be electrically connected to the input 641 b of the secondfluid pressure source, such that a single activation signal activateseach of the at least two impedance reduction systems 601, 602substantially simultaneously. Should one of the redundant impedancereduction systems 601, 602 fail to operate (either partially orcompletely), the other can still operate to dispense conductive gel ontothe exposed surface of the electrode. The activation signal provided tothe input 641 a of the first fluid pressure source 640 a may be providedby the control unit 120 (FIG. 1) to the first fluid pressure source 640a using an electrical conductor that is physically distinct from thatwhich provides the activation signal to the input 641 b of the secondfluid pressure source 640 b to permit further redundancy, for example,should one of the electrical conductors be damaged. Alternatively, asingle electrical conductor may be provided between the control unit 120and the electrode assembly, with the single electrical conductor beingconnected to both the input 641 a of the first fluid pressure source 640a and the input 641 b of the second fluid pressure source 640 b.

It should be appreciated that each of the first and second pressuresources 640 a, 640 b may alternatively receive separate activationsignals, as the present invention is not limited to receiving a singleactivation signal. The separate activation signals may be sent, forexample by the control unit 120, to each of the first fluid pressuresource 640 a and the second fluid pressure source 640 b at substantiallythe same time, or at different times. For example, a first activationsignal may be provided to the input 641 a of the first fluid pressuresource 640 a at a first time, and a second activation signal may beprovided to the input 641 b of the second fluid pressure source 640 b ata second time that is subsequent to the first time. In accordance withone embodiment, the control unit 120 (FIG. 1) may send the firstactivation signal to the first fluid pressure source 640 a at a firsttime, and send the second activation signal to the second fluid pressuresource 640 b at a second and subsequent time where it is determined thatthe first impedance reduction system 601 failed to operate.Alternatively, the second activation signal may be sent to the secondfluid pressure source 640 b at a second and subsequent time even whereactivation of the first fluid pressure source 640 a is successful. Sucha subsequent activation of the second fluid pressure source 640 b wouldpermit a second deployment of conductive gel onto the exposed surface ofthe electrode and permit the electrode to maintain a high conductivitywith the patient for a longer period of time than if both impedancereduction systems 601, 602 were activated at substantially the sametime.

FIG. 9 illustrates a therapy electrode assembly that combines one ormore ECG sensing electrodes, a therapy electrode, and redundantimpedance reduction systems in a single integrated electrode assembly inaccordance with a further aspect of the present invention. As shown, theelectrode assembly 600 includes a pair of ECG sensing electrodes 612 a,612 b for monitoring the cardiac function of a patient. The electrodeassembly 600 further includes a therapy electrode 614, and at least twoimpedance reduction systems 601, 602, similar to those describedpreviously with respect to FIG. 8. It should be appreciated that in analternative embodiment, only a single impedance reduction system may beprovided. The pair of ECG sensing electrodes 612 a, 612 b may beelectrically separated from the therapy electrode 614, for example, byan insulator. It should be appreciated that in other embodiments, theelectrode assembly 600 may include only a single ECG sensing electrode,while in other embodiments, more than two ECG sensing electrodes may beprovided. In such alternative embodiments, the number and placement ofECG sensing electrodes and may vary from that shown in FIG. 9. Theelectrode assembly 600 may include one or more sections 605 a which mayinclude one or more gel reservoirs and/or fluid channels, and which maybe at least partially separated from one or more other sections 605 aand/or sections 605 b which may include the sensing electrodes 612 a,612 b and/or pressure sources 640 a, 640 b. The one or more sections 605a, 605 b may be at least partially physically separated from one anotherby slots and/or gaps as described above with reference to FIGS. 3A-3D.

In yet a further embodiment, the integrated electrode assembly caninclude additional sensors 616, other than the one or more ECG sensingelectrodes and the therapy electrode, that are capable of monitoringother physiological parameters of a patient, such as blood pressure,heart rate, thoracic impedance, pulse oxygen level, respiration rate,heart sounds, etc.

The electrode assembly 600 may be worn on the patient's body such thatone of the pair of ECG sensing electrodes 612 a, 612 b is disposedapproximately in the center of the patient's torso, and the other of thepair of ECG sensing electrodes 612 a, 612 b is disposed on the side ofthe patient's torso. For example, as shown in FIG. 10, the electrodeassembly 600 may be worn on the front of the patient's torso, so thatthe ECG sensing electrode 612 a is disposed approximately in the centerof the patient's chest, and the other ECG sensing electrode 612 b isdisposed on the patient's side. A second electrode assembly 600′ may beworn on the back of the patient's torso to provide a second pair of ECGsensing electrodes 612 a′, 612 b′, so that one of the ECG sensingelectrodes (e.g., ECG sensing electrode 612 a′) of the second pair ofECG sensing electrodes 600′ is disposed approximately in the center ofthe patient's back, and the other ECG sensing electrode (e.g., ECGsensing electrode 612 b′) of the second pair of ECG sensing electrodes600′ is disposed on the patient's side opposite the other ECG sensingelectrode (e.g., ECG sensing electrode 612 b) of the first pair of ECGsensing electrodes 612 a, 612 b, as shown in FIG. 10. Such anarrangement provides a front-to-back pairing of ECG sensing electrodes(e.g., 612 a, 612 a′) and a side-to-side pairing of ECG sensingelectrodes (e.g., 612 b, 612 b′). It should be appreciated that otherplacements for the first electrode assembly 600 and the second electrodeassembly 600′ may alternatively be used. For example, the firstelectrode assembly 600 may be placed on one side of the patient's torso,and the second electrode assembly 600′ placed on the other side of thepatient's torso to provide side-to-side pairings of ECG sensingelectrodes.

Having thus described several aspects of at least one embodiment of thisinvention, it is to be appreciated various alterations, modifications,and improvements will readily occur to those skilled in the art. Suchalterations, modifications, and improvements are intended to be part ofthis disclosure, and are intended to be within the scope of theinvention. Accordingly, the foregoing description and drawings are byway of example only.

What is claimed is:
 1. A therapy electrode system comprising: asubstrate including a plurality of conductive gel reservoirs includingan electrically conductive gel disposed on a first side thereof, a firstof the plurality of conductive gel reservoirs disposed in a firstsegment of the substrate and a second of the plurality of the conductivegel reservoirs disposed in a second segment of the substrate, the firstsegment of the substrate configured to move at least partiallyindependently from the second segment of the substrate; a fluid channelin fluid communication with a fluid pressure source, the first of theplurality of conductive gel reservoirs, and the second of the pluralityof the conductive gel reservoirs; and one of a slot or a gap passingthrough the substrate and extending from a region proximate the fluidchannel and between the first of the plurality of conductive gelreservoirs and the second of the plurality of the conductive gelreservoirs to an edge of the substrate distal from the fluid channel,the one of the slot or the gap physically separating at least a portionof the first segment of the substrate from the second segment of thesubstrate.
 2. The electrode system of claim 1, further comprising anelectrically conductive layer having a first surface disposed on asecond side of the substrate and having a second surface configured tobe disposed adjacent to a patient's skin.
 3. The electrode system ofclaim 2, wherein the plurality of conductive gel reservoirs and thefluid channel are included in a first impedance reduction systemconfigured to dispense a first amount of a first electrically conductivegel onto the second surface of the electrically conductive layer inresponse to a first activation signal, and wherein the electrode systemfurther includes a second impedance reduction system configured todispense a second amount of a second electrically conductive gel ontothe second surface of the electrically conductive layer in response to asecond activation signal.
 4. The electrode system of claim 3, whereinthe first impedance reduction system is similar in construction to thesecond impedance reduction system.
 5. The electrode system of claim 1,further comprising a garment wearable on a torso of a patient, thegarment including a pocket formed from a layer of fabric and configuredto receive the electrode system, wherein the electrode system isconfigured to dispense an amount of the conductive gel through the layerof fabric and into contact with the patient's skin.
 6. The electrodesystem of claim 5, further comprising an electrically conductive layerdisposed on a second side of the substrate, the electrically conductivelayer including a plurality of apertures configured to dispense theamount of the conductive gel.
 7. The electrode system of claim 5,further comprising an electrically conductive pathway included in thelayer of fabric, the electrically conductive pathway configured todeliver electrical energy to the patient's skin through the amount ofconductive gel dispensed from the electrode system.
 8. The electrodesystem of claim 5, wherein the layer of fabric is formed from anelectrically conductive material.
 9. The electrode system of claim 5,wherein each of the substrate and the pocket are tapered to permit theelectrode system to be received in the pocket in only a singleorientation.
 10. The electrode system of claim 1, further comprising atleast one ECG sensing electrode configured to monitor an ECG signal of apatient, the at least one ECG sensing electrode being disposed on asecond side of the substrate and electrically insulated from portions ofthe electrode system configured to receive the conductive gel.
 11. Theelectrode system of claim 10, further comprising at least one additionalsensor configured to monitor a physiological parameter of the patientother than an ECG signal of the patient.
 12. The electrode system ofclaim 11, wherein the at least one additional sensor is disposed on athird segment of the substrate, the third segment of the substrate atleast partially physically separated by one of a slot or a gap definedin the substrate from portions of the substrate on which the pluralityof conductive gel reservoirs are disposed.
 13. The electrode system ofclaim 1, wherein the substrate further comprises a plurality ofadditional segments positioned adjacent to one another and at leastpartially physically separated from one or another by slots or gapsdefined in the substrate, each of the plurality of additional segmentsincluding a conductive gel reservoir disposed on first side thereof. 14.The electrode system of claim 1, wherein the fluid pressure source isdisposed on a third segment of the substrate, the third segment of thesubstrate being at least partially physically separated by one of a slotor a gap defined in the substrate from portions of the substrate onwhich the plurality of conductive gel reservoirs are disposed.
 15. Theelectrode system of claim 1, wherein the substrate is tapered from afirst end to a second end, the taper of the substrate preventinginsertion of the electrode system into a tapered pocket of a wearablemedical device in an undesired direction.
 16. The electrode system ofclaim 1, further comprising a magnet disposed on a portion of thesubstrate and configured to apply a force to a magnet disposed on apocket of a garment in which the electrode system can be inserted, theapplied force providing an indication of proper orientation of theelectrode system in the pocket.
 17. The electrode system of claim 1,further comprising a snap disposed on a portion of the substrate andconfigured to engage a corresponding snap disposed on a pocket of agarment in which the electrode system can be inserted, the engagement ofthe snap with the corresponding snap providing an indication of properorientation of the electrode system in the pocket.
 18. The electrodesystem of claim 1, wherein the substrate comprises a fabric permeable toconductive gel which the electrode system is configured to dispense. 19.The electrode system of claim 1, wherein the substrate is perforated.20. The electrode system of claim 1, wherein the electrode systemincludes an indicator disposed on an externally visible surface of theelectrode system and configured to visually indicate whether the fluidsource has been actuated.